On-chip test pattern generation

ABSTRACT

A chip is provided that includes an integrated circuit including a plurality of logic elements, wherein the plurality of logic elements is configured to form, in a test mode, a plurality of scan chains. The chip further includes an on-chip signal generator connected with the integrated circuit and configured to provide, in the test mode, a test pattern signal to the plurality of scan chains.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Application number EP 15188 790.8, filed on Oct. 7, 2015, the contents of which are hereinincorporated by reference in its entirety.

FIELD

Various embodiments relate to a chip comprising an on-chip signalgenerator configured to provide, in a test mode, a test pattern signalto a plurality of scan chains formed by a plurality of logic elements.Various embodiments relate to a burn-in oven and a method.

BACKGROUND

To test an integrated circuit (IC), it is known to subject logicelements of the IC to a stress test. E.g., the chip comprising the ICcan be placed in a burn-in oven where environmental conditions can becontrolled. E.g., an elevated temperature can be applied.

In reference implementations, an Automated Test Pattern Generation(ATPG) pattern signal which is loaded into the burn-in oven and, fed toIC via scan pins, to the logic elements. The ATPG signal is apseudorandom test pattern which intends to toggle all or at least amajority of the logic elements between the available states. Tofacilitate toggling, a test mode can be triggered which effects logicalinterconnections between the logic elements subject to the test; thelogical interconnections enable a series of logic elements to act as ashift register (scan chain) where different clocked states of the ATPGsignal iteratively toggle the logic elements of a scan chain. Then, thestates of the logic elements of the scan chains may be read out andcompared to expected values. Thereby, failure or wear-out of thehardware elements forming the logic elements, e.g., of the transistors,can be detected.

However, such scenarios face certain restrictions and drawbacks. E.g.,there may be limited space available in the burn-in oven to store ATPGpatterns. On the other hand, it may be required to provide the ATPGsignal having a comparably large number of input pins to ensure thatalmost all or all logic elements are toggled. This requires significantefforts in signal routing which may be complex due to the limited spaceavailable.

SUMMARY

Therefore, a need exists for advanced techniques of test patterngeneration for a test mode. In particular, a need exists for suchtechniques which enable the test mode with reduced signal routingrequirements.

This need is met by the features of the independent claims. Thedependent claims define embodiments.

According to an aspect, a chip is provided. The chip comprises an IC.The IC comprises a plurality of logic elements. In a test mode, theplurality of logic elements is configured to form a plurality of scanchains. The chip further comprises an on-chip signal generator connectedwith the chains. In the test mode, the signal generator is configured toprovide a test pattern signal to the plurality of scan chains.

According to an aspect, a burn-in system is provided. The burn-in systemcomprises a burn-in oven and a receptacle. The receptacle is arranged isconfigured to releasably mount a chip according to a further aspect. Theburn-in system further comprises an IEEE Test Access Port Connectorconfigured to trigger a test mode.

According to an aspect, a method is provided. The method comprises aplurality of logic elements of an IC forming, in a test mode, aplurality of scan chains. The method further comprises an on-chip signalgenerator providing, in the test mode, a test pattern signal to theplurality of scan chains.

It is to be understood that the features mentioned above and featuresyet to be explained below can be used not only in the respectivecombinations indicated, but also in other combinations or in isolation,without departing from the scope of the present disclosure. Features ofthe above-mentioned aspects and embodiments may be combined with eachother in other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and additional features and effects of the disclosure willbecome apparent from the following detailed description when read inconjunction with the accompanying drawings, in which like referencenumerals refer to like elements.

FIG. 1 schematically illustrates a burn-in system comprising a burn-inoven.

FIG. 2 schematically illustrates a chip according to variousembodiments, the chip comprising an on-chip signal generator coupledwith an IC of the chip.

FIG. 3 schematically illustrates details of the signal generator of FIG.2 which is implemented as a linear feedback shift register according tovarious embodiments.

FIG. 4 schematically illustrates a chip according to variousembodiments, the chip comprising an on-chip signal generator coupledwith an IC of the chip and further comprising a decompressor coupledin-between the signal generator and the IC.

FIG. 5 schematically illustrates a chip according to variousembodiments, the chip comprising an on-chip signal generator coupledwith an IC of the chip, wherein the chip comprises a switch and aplurality of external scan control pins.

FIG. 6 schematically illustrates the switch of FIG. 5 in greater detail.

FIG. 7 is a flowchart of a method according to various embodiments.

DETAILED DESCRIPTION

In the following, embodiments of the disclosure will be described indetail with reference to the accompanying drawings. It is to beunderstood that the following description of embodiments is not to betaken in a limiting sense. The scope of the disclosure is not intendedto be limited by the embodiments described hereinafter or by thedrawings, which are taken to be illustrative only.

The drawings are to be regarded as being schematic representations andelements illustrated in the drawings are not necessarily shown to scale.Rather, the various elements are represented such that their functionand general purpose become apparent to a person skilled in the art. Anyconnection or coupling between functional blocks, devices, components,or other physical or functional units shown in the drawings or describedherein may also be implemented by an indirect connection or coupling. Acoupling between components may also be established over a wirelessconnection. Functional blocks may be implemented in hardware, firmware,software, or a combination thereof.

Hereinafter, techniques of on-chip test pattern signal generation areexplained. These techniques may facilitate on-chip ATPG. Thesetechniques may be applied for burn-in exercises of an IC.

According to embodiments, a chip is provided. The chip comprises an IC.The IC comprises a plurality of logic elements. In a test mode, theplurality of logic elements is configured to form a plurality of scanchains. The chip further comprises an on-chip signal generator connectedwith the IC. In the test mode, the signal generator is configured toprovide a test pattern signal to the plurality of scan chains.

Each one of the plurality of logic elements may be formed by one or moretransistors, e.g., implemented in CMOS technology. As such, due tomanufacturing spread, etc., some of the transistors may be subject tofailure. Hereinafter, techniques are illustrated which enable toidentify failing transistors and, thus, failing logic elements in aconvenient and yet reliable manner. Techniques are illustrated whichenable to test combinational and sequential logic. Connectivity, open,shorts, and resistivity between the logic elements may be tested.

The scan chains may form shift registers. The scan chains may formlogical interconnections in-between the various logic elements. In somescenarios, each one of the plurality of logic elements may be part of asingle scan chain. Hereinafter, for illustrative purposes, reference ismade primarily to the logic elements being implemented by flip flops.However, in various scenarios, respective techniques may be readilyapplied to different kinds and types of logic elements, e.g., includingsequential logic such as flip flops and combinational logic such asgates, multiplexers, etc.

The scan chains may facilitate toggling each one of the plurality oflogic elements. E.g., toggling may occur in a clocked manner. For this,a clock signal may be employed. For each cycle, the test pattern signalmay indicate a different codeword. The number of codewords of the testpattern signal is sometimes referred to as cycle length. The cyclelength may be larger than a length of the codeword. E.g., there may bemore than 100.000 cycles, or more than 1.000.000 cycles, or more than10.000.000 cycles. E.g., the codeword may have a length of less than 10,or less than 100 bit. Each position of the codeword is associated withone of the plurality of scan chains. For each cycle, the current valueof the respective position of the codeword is fed to an entry point ofthe respective scan chain.

The IC may be selected from the group comprising: an analoguetransceiver stage; a digital transceiver stage; a Gigabit PassiveOptical Network (GPON) IC; a Central Office (CO) IC; a Customer PremisesEquipment (CPE) IC; a sensor; a wireless transceiver; etc. The IC maycomprise elements selected from the group comprising: a processor; aworking memory; a non-volatile memory. The IC may comprise digital,analogue and/or mixed digital-analogue elements. The IC may compriseradio frequency (RF) functionality. In particular, the IC may relate toInternet of Things (IoT) and/or Connected Home applications. The IC maycomprise more than 100.000 transistors, preferably more than 1.000.000transistors. The IC may form a system-on-a-chip (SOC).

The on-chip signal generator may thus be formed on the same die as theIC. There may be routing provided in between the signal generator andthe IC. In some scenarios, the signal generator may be provided in thesame package as the IC. The signal generator may also be provided in adifferent package than the IC. The signal generator may be comparablylimited in complexity. E.g., the signal generator may comprise less than100.000 transistors, preferably less than 1.000 transistors, morepreferably less than 500 transistors. Thereby, a cost effectiveimplementation of the signal generator becomes possible.

By providing the on-chip signal generator, it is not required toprovision external routing of the test pattern signal during the testmode. In scenarios where restricted space is available for externalrouting, this can facilitate execution of the test mode.

The test mode may enable testing of functionality of the IC prior toplacing the IC in service. The specific type of the test mode that canbe implemented by the test pattern signal is not germane for thefunctioning of the signal generator. Various types and kinds of testmodes may be employed. In the various scenarios disclosed herein, aspecific test mode of relevance is the burn-in test mode.

FIG. 1 illustrates aspects with respect to a burn-in exercise of theplurality of flip flops. A burn-in system 101 comprises a burn-in oven102 which, according to reference implementations, has wiring 111 routedfrom the exterior to its interior. The burn-in oven has limiteddimensions. In the interior of the burn-in oven, a device under test(DUT) such as a chip 110 comprising an IC is mounted by a receptacle(not shown in FIG. 1).

Connecting the wiring 111 with respective scan control pins of the chip110 can be time-consuming and cumbersome. The time for setting up thetest (test setup time) can be long.

According to various scenarios as disclosed herein, various scenariosenable to greatly reduce the test setup time. Only a comparably smallernumber of wiring typically needs to be connected with the chip 110according to various scenarios disclosed herein.

In various scenarios disclosed herein, it may only be required toconnect wiring corresponding to an Institute of Electrical andElectronics Engineers (IEEE) 1149.1 test access port (TAP) connector, asspecified by the Joint Test Action Group (JTAG). It may not be requiredto connect wiring corresponding to an ATPG test signal externallygenerated.

After setup of the test is completed and when executing the burn-intest, a defined temperature or temperature profile is applied in theinterior of the burn-in oven 102 for a test time. During the test time,the various flip flops of the chip 110 are toggled. A failure-rate curvedescribing the number of finally failing flip flops as a function ofoperation time can thus be sampled in accelerated time lapse. Weakdevices thus tend to finally fail during the test time.

FIG. 2 illustrates aspects of an on-chip signal generator 220. Ingeneral, various types of signal generators may be employed. E.g., asingle flip flop may be employed in combination with a feedback branchand one or more inverters arranged in output branches. Hereinafter,various scenarios will be described with respect to the signal generatorbeing implemented as a linear feedback shift register (LFSR). However,in all scenarios disclosed herein it is possible to replace the LFSR byanother suitable type of signal generator.

In the scenario of FIG. 2, the signal generator 220 is implemented bythe LFSR. The LFSR 220 is connected with the IC 230. The IC 230comprises a plurality of flip flops 231. Because the IC 230, as depictedin FIG. 2, is operated in the test mode, the flip flops 231 form scanchains 232.

In the scenario of FIG. 2, three, M=3, scan chains are formed by theplurality of flip flops 231. This is illustrative only and a smaller orlarger number of scan chains 232 may be formed. The number of scanchains 232 is not germane for the functioning of the techniquesaccording to various scenarios disclosed herein. E.g., in examples theremay be 285 scan chains.

The LFSR 220 outputs a test pattern signal 281. Referring to FIG. 3, thetest pattern signal 281 comprises—for each cycle of a clock signal 271received via a respective external pin 211—a respective codeword 321.Different cycles correspond generally to different codewords 321. Inother words, the LFSR 220 is configured to output different states ofthe test pattern signal 281 depending on the clock signal 271.

The codeword 321 comprises an entry for each one of the scan chains 232.Thus, in the scenario of FIGS. 2 and 3, the codeword 321 has a lengththree, N=3. As can be seen, M=N. This enables to test all differentkinds of combinations of states of the various flip flops 231. Thisfacilitates an effective stress test.

FIG. 3 illustrates aspects of the LFSR 220 in greater detail. The LFSR220 comprises three flip flops 300 (labelled “A”, “B”, and “C” in FIG.3), feedback branches 301, a converter 302 which is configured toconvert the signals obtained via the feedback branches based on a linearfunction to obtain a transformed feedback signal, and a further feedbackbranch 303 configured to provide the transformed feedback signal to aninput of the first flip flop 300. The state of each flip flop 300 isassociated with an entry of the codeword 321. The LFSR 220 provides thetest pattern signal in a pseudorandom fashion depending on a seed whichis used to initialize the LFSR 220. After some cycle length, thecodewords 321 are repeated.

Again referring to FIG. 2, e.g., the pin 211 may be an external testmode pin. E.g., the pin 211 may be part of the TAP connector. E.g., thepin 211 may be the TAP Test Clock (TCK) pin. In other scenarios, the pin211 may be a proprietary pin.

E.g., the wiring 211 may be connected to the various external pinsdisclosed herein via a burn-in board 105 comprising one or more socketsfor one or more chips, or via a needle card, or via wire bonds or thelike. The various external pins may comprise a metallic pad that isaccessible from the outside. E.g., the metallic pad may have dimensionsof more than 50 μm×50 μm. E.g., the burn-in board 105 may have limiteddimensions due to the limited dimensions of the burn-in oven.

The clock signal 271 is also provided to the IC 230. Depending on thetest pattern signal 281 and further depending on the clock signal 271,the flip flops 231 toggle through different states. Here, the scanchains 232 may function as shift registers such that a particular stateof the flip flops 231 propagates through the scan chains 232 as theclock signal 271 advances. During read-out, the states of the variousflip flops 231 can be retrieved. Typically, read-out is not required totake place in the burn-in oven 102.

FIG. 4 illustrates aspects regarding the length of the codeword 321 ofthe test pattern signal 281. In the scenario of FIG. 4, there is—forillustrative purposes—a number of M=4 four scan chains 323. Yet, thecodeword 321 has a length of N=3 three. Thus, N<M. The chip 110 furthercomprises a decompressor 271 configured to translate the (compressed)test pattern signal 281 into a decompressed test pattern signal 282which has a longer codeword length. In particular, the decompressed testpattern signal 282 has a codeword length equalling the number M=4 ofscan chains 232. By configuring the LFSR 220 to output a codeword 321 ofcomparably small length, a simpler and cost-effective implementation ofthe LFSR 220 becomes possible. E.g., in an example there may be M=285scan chains 232 and the codeword length of the compressed test patternsignal 281 may be N=6; the codeword length of the uncompressed testpattern signal 282 may be 285 as well.

A decompressor may be provided in the various scenarios as disclosedherein, albeit not specifically mentioned. The decompressor mayfacilitate the read-out.

FIG. 5 illustrates aspect with respect to selectively enabling the testmode. In FIG. 5, an external test mode pin 213 is provided. The externaltest mode pin 213 is connected with the LFSR 220 and the IC 230. Via theexternal test mode pin 213, a setup signal 271 may be received. E.g.,the external test mode pin 213 may be part of the TAP. E.g., theexternal test mode pin 213 may be the Test Mode Select (TMS) pin of theTAP.

The setup signal 271 may trigger the test mode. Once the setup signal271 indicates that the test mode is triggered, one or more of thefollowing actions may be taken:

E.g., the LFSR 220 may be initialized, e.g., by specifying the seed. Theflip flops 231 may be configured to form the scan chains 232. In FIG. 5,a switch 291 is provided. The switch 291 can be controlled by the setupsignal 271. If the setup signal 281 indicates the test mode, the switchmay connect the external clock pin 211 with the IC 230, i.e., with thescan chains 232 and the flip flops 231. In other modes—different to thetest mode—the switch 291 may disconnect the external clock pin 211 fromthe IC 230. E.g., during normal operation or during a further test mode,the switch 291 may disconnect the external clock pin 211 from the IC230.

By means of the setup signal 271, it becomes possible to selectivelyoperate the IC 230 in the test mode during device testing. Normaloperation is not inhibited.

The chip 110 also comprises a further switch 290, e.g., implemented by amultiplexer. The further switch 290 is configured to selectively connectthe LFSR 220 with the IC 230. The further switch 290 may be controlledat least by the setup signal 272. In particular, the further switch 290is configured to connect the LFSR 220 with the IC 230 in the test mode;and to disconnect the LFSR 220 from the IC 230 in a further modedifferent to the test mode.

FIG. 5 also illustrates aspects with respect to a further test mode.Sometimes, it may be desirable to enable one or more further test modes.In particular, it may be desirable that the further test modes do notrely on the LFSR 220.

E.g., the further switch 290 can be optionally configured to connect aplurality of external scan control pins 214 (for simplicity, in FIG. 5only a single external scan control pin 214 is graphically illustrated)in a further test mode with the IC 230. It may be possible to writeand/or read out data from the plurality of flip flops 231 via theplurality of external scan control pins 214. E.g., a further testpattern signal may be provided to the scan chains 232 via the pluralityof external scan control pins 214. E.g., a further clock signal may beprovided to the plurality of scan chains 232 via the external scancontrol pins 214; e.g., each one of the plurality of flip flops 231 maybe configured to toggle through different states depending on thefurther clock signal and further depending on the further test patternsignal. E.g., after the burn-in test has finished, it may be possible toread out data from the plurality of flip flops 231 via the plurality ofexternal scan control pins 214, thereby testing whether all flip flops231 are responding or whether some of the flip flops 231 have failed.E.g., a respective compressor and/or decompressor may be provided withrespect to data communicated via the plurality of external scan controlpins 214.

The external scan control pins 214 may be provided in the variousscenarios as disclosed herein, albeit not specifically mentioned.

The external scan control pins 214 facilitate execution of variousfurther tests, beyond the test mode implemented by the LFSR 220.

Typically, to enable testing of various kinds, the scan chains 232 arerequired to be formed by the flip flops 231. This may be done by settinga “SCAN_ENABLE” port of the IC 230 to ONE.

FIG. 6 illustrates detailed aspects with respect to forming the scanchains 232. Depending on the setup signal 272, a switch applies either alogical “ONE”, “ZERO” to the “SCAN_ENABLE” port. E.g., if the setupsignal 272 indicates the test mode, then the “ONE” may be applied andthe scan chains 232 may be formed. If the setup signal 272 indicatesnormal operation, then the “ZERO” may be applied. If the setup signal272 indicates the further test mode, then connection with at least oneof the plurality of external scan control pins 214 may be established.Then, the formation of the scan chains 232 may be selectively triggeredvia the respective at least one of the plurality of external scancontrol pins 214. E.g., the switch of FIG. 6 may be implemented asmultiplexer.

FIG. 7 is a flowchart of a method according to various embodiments.First, the test mode—in the scenario of FIG. 7 the burn-in mode—isenabled, 901. For this, the burn-in board 105 may be employed to contactthe chip 110 in the burn-in oven 102. Then, the setup signal 272 mayindicate a respective value. The setup signal 272 may be providedemploying the JTAG TAP within the IEEE JTAG framework and may beprovided via the burn-in board 105. Here, the LFSR 220 may beinitialized with a respective seed. The clock signal 271 may be providedto the IC 230.

Next, 902, the IEEE JTAG state machine is brought to state runtest/idle; this step is optional and may be particularly relevant in theIEEE JTAG framework.

Then, the LFSR 220 provides the test pattern signal 281, 903. This maybe done via the TCK pin of the JTAG TAP. This causes the various flipflops 231 being toggled into different states. This may occur atelevated temperature within the burn-in oven 102. The scan chains 232function as shift registers. 903 may be executed for a predefined testtime to trigger ageing and wear out of the various transistors of the IC230.

901-903 all contribute to the burn-in test mode 1001.

Then, it is checked whether some of the flip flops 231 failed due to theburn-in test, 904. This may be done by reading out data via theplurality of scan control pins 214, e.g., outside the burn-in oven 102.E.g., in some scenarios the state of the flip flops 231 forming the scanchains 232 after the burn-in test has finished may be read out. I.e., itmay be possible to test the impact of the stress test of 903.

If the check 904 passes, the chip 110 may be released for normaloperation 1002, 905.

Summarizing, above techniques have been illustrated which enable toreduce the scan setup time. A test pattern signal is not required to beexternally fed to a chip, but is rather generated on-chip. A LFSR may beemployed for generating the test pattern signal.

Although the disclosure has been shown and described with respect tocertain embodiments, equivalents and modifications will occur to othersskilled in the art upon the reading and understanding of thespecification. The present disclosure includes all such equivalents andmodifications and is limited only by the scope of the appended claims.

The invention claimed is:
 1. A chip, comprising: an integrated circuitcomprising a plurality of logic elements, wherein the plurality of logicelements is configured to form, in a test mode, a plurality of scanchains, and an on-chip signal generator connected with the integratedcircuit and configured to provide, in the test mode, a test patternsignal to the plurality of scan chains, wherein the on-chip signalgenerator is configured to provide the test pattern signal having acodeword length N, and wherein plurality of logic elements is configuredto form M scan chains, wherein N is smaller than M, and wherein the chipfurther comprises a decompressor configured to translate the testpattern signal having the codeword length of N into a decompressed testpattern signal having a codeword length of M, or wherein the on-chipsignal generator is configured to provide the test pattern signal havinga codeword length of N, wherein the plurality of logic elements isconfigured to form M scan chains, and wherein N equals M.
 2. The chip ofclaim 1, wherein the on-chip signal generator comprises a linearfeedback shift register.
 3. The chip of claim 1, wherein the on-chipsignal generator comprises less than 100,000 transistors.
 4. The chip ofclaim 1, further comprising: an external test mode pin connected withthe on-chip signal generator and the integrated circuit, wherein theon-chip signal generator is configured to initialize in response toreceiving a setup signal via the external test mode pin, and wherein theplurality of logic elements is configured to form the scan chains inresponse to receiving the setup signal via the external test mode pin.5. The chip of claim 4, further comprising: an external clock pinconnected with the on-chip signal generator and selectively connectedwith the integrated circuit, wherein the on-chip signal generator isconfigured to provide different states of the test pattern signaldepending on a clock signal received via the external clock pin, whereineach one of the plurality of logic elements is configured to togglethrough different states depending on the clock signal and the testpattern signal, and wherein an IEEE Test Access Port comprises theexternal clock pin and the external test mode pin.
 6. The chip of claim1, wherein the test mode is a burn-in exercise of the plurality offlip-flops.
 7. A chip, comprising: an integrated circuit comprising aplurality of logic elements, wherein the plurality of logic elements isconfigured to form, in a test mode, a plurality of scan chains, and anon-chip signal generator connected with the integrated circuit andconfigured to provide, in the test mode, a test pattern signal to theplurality of scan chains; an external clock pin connected with thesignal generator and selectively connected with the integrated circuit,wherein the on-chip signal generator is configured to provide differentstates of the test pattern signal depending on a clock signal receivedvia the external clock pin, and wherein each one of the plurality oflogic elements is configured to toggle through different statesdepending on the clock signal and the test pattern signal.
 8. The chipof claim 7, further comprising: at least one switch configured toconnect, in the test mode, the external clock pin with the integratedcircuit and configured to disconnect, in a further mode different to thetest mode, the external clock pin from the integrated circuit.
 9. Achip, comprising: an integrated circuit comprising a plurality of logicelements, wherein the plurality of logic elements is configured to form,in a test mode, a plurality of scan chains, and an on-chip signalgenerator connected with the integrated circuit and configured toprovide, in the test mode, a test pattern signal to the plurality ofscan chains; a plurality of external scan control pins selectivelyconnected with the integrated circuit, and at least one switchconfigured to disconnect, in the test mode, the plurality of externalscan control pins from the plurality of scan chains, wherein the atleast one switch is configured to connect, in a further mode other thanthe test mode, the plurality of external scan control pins to theplurality of scan chains.
 10. The chip of claim 9, wherein the pluralityof external scan control pins is further configured to provide a furtherclock signal to the plurality of scan chains, and wherein each one ofthe plurality of logic elements is configured to toggle throughdifferent states depending on the further clock signal and the furthertest pattern signal.